Apparatus for removing dust and granular material from asbestos fibre



Nov. 19, 19 w. D. SHELDON, JR

APPARATUS FOR REMOVING DUST AND GRANULAR MATERIAL FROM ASBESTOS FIBRE Filed Dec. 16, 1952 4 SheetsSheet 1 Nov? 1957 w. D. SHELDON, JR

APPARATUS FOR REMOVING DUST AND GRANULAR MATERIAL FROM ASBESTOS FIBRE 4 Sheets-Sheet 2 Filed Dec. 16, 1952 Illlll llll.

Nl/ENTOR Ca-Juug Info. HJTQRNE BY Jahw Nov. 19, 1957 w. D. SHELDON, JR 2,813,306

APPARATUS FOR REMOVING DUST AND GRANULAR MATERIAL FROM ASBESTOS FIBRE Filed Dec. 16. 1952 4 Sheets-Sheet 3 MLL/AIM- AIS/15mm R. :ByJ

- Nov. 19, 1957 w. D. SHELDON, JR 2,813,306 APPARATUS FOR REMOVING DUST AND GRANULAR MATERIAL FROM ASBESTOS FIBRE Filed Dec. 16, 1952 4 Sheets-Sheet 4 Q United States Patent C) APPARATUS FOR REMOVING DUST AND GRANU- LAR MATERIAL FROM ASBESTOS FIBRE William D. Sheldon, In, Galt, Ontario, Canada Application December 16, 1952, Serial No. 326,239.

5 Claims. (CI. 19-90) This invention relates to a method and apparatus for cleaning asbestos fibre. Asbestos fibre is released from the host rock in which it occurs by crushing the rock to set free bundles of fibre, which bundles are then opened or fluffed-up by a rubbing actionor by a gentle abrading. The release of the fibre may be carried out in the same operation as opening of the fibre bundles, or the bundles may first be released and then opened separately in a different operation. In either event, the open fibre will always contain a considerable amount of dust and granular material which must be removed from it before the fibre can be used commercially. Asbestos fibre is very delicate and any working tends to break down the longer fibres into less valuable shorter fibres. Thus, since the value of the fibre depends upon its length, great care must be taken to insure that in removing the dust and granular material the fibre length is not shortened, and the value of the product consequently reduced. 1

Up to the present time, no entirely satisfactory means have been available for removing dust and granularmaterial from the fibre without breaking down some of the fibre, and the consequent loss in value of the product has generally been accepted in the industry as a necessary evil.

The present invention provides a novel method and apparatus for accomplishing the removal of dust and granu- .lar material from asbestos fibre with a minimum of work being done on the fibre itself and with a consequent minimum of reduction in fibre length during theoperation.

The method of the present invention consists essentially in depositing the dirty fibre on a screen through which air is being drawn, which screen has suitableopenings for retaining the fibre but permitting the dust and granular material to pass through. The air flow through the screen is then briefly reversed lifting the fibre from the screen and allowing it almost immediately to redeposit. This operation is repeated a relatively large number of times and each time the fibre redeposits, more of the dust and granular material will be carried through the screen, eventually leaving the fibre completely free of dust and granular material. The flow of air over andthrough the screen is controlled and directed in such a fashion that each time the fibre is lifted from the screen, itis carried a certain distance towards a point of withdrawal from the apparatus before it is redeposited. Thus, the process, may be carried out continuously without any moving parts coming in contact with the fibre itself. t

The novel apparatus of the invention which is arranged to carry out the above process consists essentially of a horizontal cylindrical drum concentrically within which is a cylindrical screen, providing an annular space between the screen and the drum wall. An air duct which conveys dirty fibre tosthe apparatus feeds in tangentially through the cylindrical wall of the drum, while cleaned fibre is continuously removed from the screen and conducted away therefrom. Dust and granular material "which pass through the screen are removed axially from the interior of the screen, at the outlet end of the apparatus. The air which enters via the inlet duct at considerable speed will follow a course around the screen within the drum before eventually being withdrawn through the central outlet at the other. end thereof. Mounted upon a shaft located on the axis of the drum and screen above referred to is at least one radial bafile arranged to be rotated in a direction corresponding to the movement of air in its helical path around the drum. This bafile extends the entire length of the screen and is arranged to sweep very close to the inner side of the screen. When the balfle is rotated at a speed which is in excess of the peripheral speed of the air following its course around the screen within the space between the screen and the drum, the pressure in front of eachbaflle as it rotates will build up while the pressure on .the following side of the baffle will be diminished; Thus, as the rotating bafile approaches a given point on the screen, ,air will be caused to flow from within the screen into the annular space between the screen and the drum, and the fibre and dust on the screen at that point will be lifted and advanced by the airstream a certain distance around the screen. When the bafiie has passed the materialthus raised, the material will once again :be deposited on the screen. Owing to the slightly different aerodynamic characteristics of the fibre and dust and granular material, the free dust and free granular material will return to the surface of the screen before the fibre which has been raised and will pass through it and be removed. In addition, the slight impact of the fibre against the screenwhen it is redeposited will loosen more {dust andgranular material which will partly then pass through thascmfin and beremoved or will be removed the next time the fibre is lifted and redeposited. This operation is repeated every time the bafile passes beneath the fibre, and it will be appreciated that whenever it is raised .fromthe screen, the fibre is carried along the path ofthe airstream until finally it arrives fully cleaned at a point on ,the screen from which it is removed and conducted away.

According to one embodiment of the invention, the screen is stationary and there are two rotating bafiies The dirty fibre is fed in an airstream tangentiallytotthe screen at one end of the apparatus and clean fibre is withdrawn from the screen at the other end thereof, the fibrepn the screen following a generally helical path has it ;;is tinte rrnittently raised and redeposited by the actionof the rotating 'baffies. j

According to another embodiment of the inventiontthe screen is rotated at a relatively slow speed, in the same direction as the rotation of the bafiles. In this embodiment, the clean fibre is removed bysuctionand carried away in an airstream. The rotation of the tsereenensures that it is progressively cleaned by the suction and the foraminations thereinremain free of ;c;1ogging.

The invention will be more fully understood from a reading of the following detailed specificationin conjunction with the accompanying drawings which illustrate several embodiments thereof, and wherein Figure 1 is a perspectiveyiewzof a preferredembodiment of the invention partlybroken away to illustrate interior details,

Figure 2 is an elevation of the apparatus illustratedwin Figure 1 showing its manner of connectionwith other components in a circuit, 1 t t Figure 3 is a fragmentary cross section of the screen in the apparatus illustrated in Figure l ,showingthe raction of the apparatus in removing dust and granular material from the fibre,

Figure 4 is a diagrammatic illustration pfithewscreen 0 illustrating the path followed by the aairstrearnand :by. :the material flowing through thewapparatus, w 1

' terior of the screen is motivated by an impeller mounted on the end of the baffle shaft,

Figure 6 is a perspective view, partly broken away, of an alternative embodiment of the apparatus according to the invention,

Figure 7 is a side elevation of a circuit layout including the embodiment of the invention illustrated in Figure 6, and

Figure 8 is a top plan view of the embodiment of the invention illustrated in Figure 5,

Figure 9 is a detailed cross section of the apparatus illustrated in Figures and 8 showing details of the air entry port and product withdrawal means.

In Figure l, 10 represents a generally cylindricalshaped casing within which is arranged concentrically a cylindrical screen 11. Between the casing 10 and the screen 11 is an annular space 12. The screen 11 is fixed to the casing 10 at the left hand end through a Z-section annular ring 13 and at the right hand end through an angle section annular ring 14. Thus, in the embodiment of Figure 1, the screen 11 is stationary.

The inlet duct (for the dirty fibre mixed in a stream of air) is shown at 15. The duct 15 discharges into the annular space 12 in a direction tangential to the screen 11. Concentric with the screen 11 is a shaft 16 mounted in bearings 17, 18 at either end of the casing 10. Bafiies 19 are fixed to the shaft 16 through members 29. Any suitable driving means, such as an electric motor as indicated at 22 in Figure 2, may be used to drive the shaft '16 and associated bafiles 19 through means such as a pulley 21 and belts at a speed which is in excess of the peripheral speed of the air travelling in the annular space 12. A damper 31 is provided in the casing 10.

The outlet duct for the cleaned fibre is shown at 23 while the outlet duct for the tailings (dust, granular material, etc.) and the air is shown at 25. The outlet duct 23 discharges into an auto-discharge trap 24 (Figure 2) from which the cleaned fibre is retrieved. The tailings along with the air are fed into a cyclone separator 26 shown in Figure 2 which separates out the tailings and discharges them into another auto-discharge trap 27, while the clean air is drawn off through duct 28 by the action of the blower 29. This clean air is discharged through the duct 30, but it may be used in further operations if desired.

The operation of the embodiment of Figure 1 will now be described and reference will be made to Figures 3 and 4.

The dirty fibre along with a quantity of air is fed to the duct 15 and sucked into the annular space 12 tangentially to the screen 11 through the action of the blower 29 (Figure 2). The dirty fibre will generally follow a helical path as indicated by the arrows 34 in Figure 4 while the air in the annular space 12 will tend to be sucked through the screen 11 and out through the outlet duct as indicated by the arrows 35 in Figure 4. As the air is sucked through the screen 11 it will tend to carry some of the dust and granular material with it. A good deal of the dust and granular material however will be held in the mat of fibres F which will form against the screen 11. In accordance with the present invention, means are provided for periodically gently lifting this mat and allowing it to' fall back against the screen. This gentle lifting and subsequent falling back against the screen will tend to tamp out the duct and granular material which is trapped in the mat. Further, because of the different aerodynamic characteristics of the fibre, on

the one hand, and the dust and granular material, on the other hand the latter will tend to fall down and go through the screen before the former has had a chance to reform as a mat. It will be understood that because of the generally helical path 34 of the material in the annular space 12, the mat will tend to move around the screen and towards the left (that is, towards the output) every time it is lifted. In other words, the periodic lifting of the mat of fibres will allow the fibres to follow the helical path 34.

The baffles 19 as stated hereinabove are rotated at a speed which is in excess of the peripheral speed of the material in the annular space 12, and are arranged to sweep very close to the inner surface of the screen 11. The baffles 19 create a back pressure and subsequent movement of air outwardly through the screen in the region immediately in front of the forward surface thereof. The inclined surface 36 (Figure 3) of the baffles 19 aids in effecting this reversal of the air flow through the screen 11. Further, there will be a region of increased inward pressure and subsequent inward flow of pressure immediately behind the trailing edge 37 (Figure 3) of the baffles 19. It will be understood that the said reversed air flow will effect the lifting of the mat referred to above, while the said increased inward flow will effect the falling back of the lifted mat. This lifting and falling back will occur each time one of the baffles 19 sweeps close to a predetermined point on the periphery of the screen 11. Thus, the fibres will follow the helical path 34 until they reach the region close to the outlet duct 23. In this region, most of the air has passed through the screen 11 so that there is little suction pressure to hold the fibres (which by this time have been cleaned) against the screen and they will tend to fall down into the outlet duct 23. The damper 31, which is situated preferably about half-Way between the inlet duct 15 and the outlet duct 23, may be employed to reduce the suction pressure in the event that the fibres still cling to the screen 11 in the region of the outlet duct 23. It will be appreciated, however, that use of the damper 31 is not essential to the operation of the device.

In Figure 6 there is shown a modification of the embodiment of Figure 1 wherein an impeller 38 having a plurality of blades 39 is arranged in the output end of the apparatus in the annular space indicated at 40 in Figure 4. It will be understood that driving means and shaft means separate from the shaft 16 would be provided so that speed of the shaft of the impeller 38 would not depend directly on the speed of the shaft 16. The impeller 38 may be employed to supply the suction pressure instead of the blower 29 of Figure 2.

The embodiment illustrated in Figures 5, 7 and 8, and 9 will now be described and like reference characters will be employed to designate parts which are the same as those of the embodiment of Figures 1, 2, 3 and 4. Whenever the parts differ slightly the subscript a will be used.

In Figure 5, 10a represents a cylindrical casing which is similar to casing 10 of Figure 1, except that the cleaned fibre outlet duct 23a is located at a different point than the duct 23 of Figure 1. Moreover, the damper 31a is slightly different from damper 31 as is apparent from a comparison of Figures 5 and 1.

One difference between the embodiment of Figure 1 and the embodiment of Figure 5 is that in Figure 5 a single baffle 19a is employed instead of the two shown in Figure 1. It will be understood, however, that any suitable number of baffles may be employed. In Figure 5 the single baffle 19a is balanced by the counterweights 41.

Another difference is that the screen 11a is rotated by means of a pulley 42, sleeve 43, and arms 44. The pulley 42 may be belted to the same motor 22 as pulley 21, as shown in Figure 8, or if preferred a separate driving means may be employed. In the embodiment of Figure 5, the screen 11a is rotated at a speed which is slow compared to the speed of the baffle 19a. (It is noted that the rotation of the screen 11a is in the same direction as the baffle 19a.)

In the embodiment of Figures 5, 7 and 8 the operation of the apparatus is basically similar to that of Figures 1, 2 and 3. The dirty fibre and a quantity of air is fed through the inlet duct a and is sucked into the annular space 12 tangentially to the screen 11a. It will be apparent from Figures 5 and 8 that the dirty fibre is admitted across the entire length of the screen 11a instead of merely the right end thereof as in Figure 1. As the fibre is lifted and redeposited on the screen 11a by the action of the battle 19a, it will follow a generally circumferential path around the screen 11a instead of the helical path previously described with reference to Figure 4. This circumferential path results from the dirty fibre being applied through the length of the screen 11a, and the cleaned fibre being taken off throughout the screen length. Generally, the fibre between admission from duct 15a to exit through duct 23a will travel only once around through the annular space 12. In the embodiment of Figure 1 the fibre might travel several times around in the annular space 12 in a helical path before being exhausted.

Since the fibre is being sucked 01f the screen 11a, care must be taken to prevent any appreciable portion of the air, which has passed through the screen 11a and which contains the dust and dirt which it is desired to remove from the fibre, from passing outwardly through the screen and out the duct 23a with the clean fibre. To prevent this from taking place, the casing 10a is curved inwardly at 50 (see Figure 9) so that it clears the screen 11a by not more than about A". The damper 31a is situated immediately below this curving-in, and the duct 23a is situated immediately below the damper. The inner ends of the damper 31a and the duct 23a also extend to with- I in about A of the screen 11a. When the damper valve 31b is opened, air will flow inwardly through the damper,

the screen 11a and into the interior of the apparatus;

most of this air, however, will short circuit as indicated by arrows 51 and pass outwardly through the screen 11a into the duct 23a, carrying with it the mat of fibres which is on the screen. Thus very little, if any, of the dirty air from inside the screen 11a which originally entered the apparatus with the dirty asbestos feed will find its way into the duct 23a.

The tailings and most of the air is exhausted through the duct 25, as previously, and it will be understood that a cyclone separator such as that shown at 26 in Figure 2 may be used to separate the tailings from the air.

Suction is applied at the outlet duct 23a by the action of the blower 45 (Figure 7). A cyclone separator 46 is employed between the outlet duct 23a and the blower 45 to separate the cleaned fibre from the air. The cleaned fibre is deposited in the auto-discharge trap 47.

Access panels through which the screen 11a may be inspected are provided at 48 and 49 as shown in Figure 8, and if desired these may be made transparent so that an operator may view the operation taking place in the apparatus.

The following information with respect to the embodiment of Figures 5, 7 and 8 is given to provide a working example:

holes per inch--each .026 inch in diameter rotating at 90 R. P. M. Bafile (19a) rotating at 530 R. P. M.

It will be appreciated, however, that suitable figures must be worked out for each particular case. The above figures are, therefore only indicative of the order of size of the various components, rates of flow and speeds of rotation.

It will also be appreciated that although I prefer, as stated above, to rotate the screen in the same direction as the bafile or baffles, the device will operate satisfactorily if the screen is rotated in the reverse direction, provided the obvious modifications to provide for this are made to the remainder of the apparatus.

What I claim as my invention is:

1. Apparatus for removing dust and granular material from asbestos fibre and the like comprising; a casing of circular cross-section; a foraminous member of circular cross-section mounted Within and concentric with said casing, and providing an annular space defined by the foraminous member on the one hand and the casing Wall on the other; inlet means for admitting an airstream containing entrained dirty asbestos fibre to said casing for deposit on the outer surface of said foraminous member; outlet means for conducting cleaned asbestos fibre away from said foraminous member; means for withdrawing an airstream and entrained dust and granular material axially from within said foraminous member at one end of said casing; a driven shaft mounted for rotation along the axis of said casing; and at least one generally radial baffle mounted on said shaft for rotation therewith, said baflle extending lengthwise of said foraminous member and being arranged to sweep close to the interior surface thereof; said shaft and battle being adapted to be rotated by suitable power means.

2. Apparatus as claimed in claim 1, in which said foraminous member is mounted for rotation about the same axis as said battle and is designed for rotation by suitable power means.

3. Apparatus as claimed in claim 2, in which said inlet means extends lengthwise of said foraminous member and is located at the lower side of the apparatus and said outlet means also extends lengthwise of said screen, and is located above and spaced apart from said inlet means; said apparatus comprising a damper extending lengthwise of said foraminous member and located immediately above said outlet means, said damper and said outlet means extending into the interior of said casing to within close proximity of said foraminous member, and said casing being curved inwardly to within close proximity of said foraminous member to meet the inner extremity of the upper side of said damper; said outlet means being adapted for connection to a source of suction.

4. Apparatus as defined in claim 1, wherein said foraminous member is a screen.

5. Apparatus as defined in claim 4, wherein said casing and said screen are cylindrical.

References Cited in the file of this patent UNITED STATES PATENTS 334,777 Hulse Jan. 26, 1886 1,930,592 Green Oct. 17, 1933 2,239,059 Schwartz et al Apr. 22, 1941 2,274,385 Schwartz et a1 Feb. 24, 1942 

